As is well known in the art, many automotive, industrial, and medical components are required to successfully pass a leak check inspection prior to assembly and use thereof. Commonly, this leak check inspection is performed by measuring pressure decay. Pressure decay provides a quantitative measure of the leak rate in cubic centimeters per minute (cm.sup.3 /min), which may be compared with an acceptable range of leak rates. Typically in automotive applications, the leak check inspection is performed on components that maintain a pressure or vacuum state during use, such as cylinder heads, cylinder blocks, transmission cases, valve covers, valve bodies, intake manifolds, exhaust manifolds, and headlight assemblies. It should be appreciated that the cost and time required to conduct leak check inspections of these components may be excessive.
In known pressure decay testing processes, a part to be tested is clamped to a testing fixture such that all fixture openings are fluidly sealed to define a sealed internal cavity or volume. The testing and clamping fixtures are custom made to fit the part being tested. Gas, such as air, is then introduced into the sealed cavity to a known pressure. The pressurized cavity is then allowed to stabilize prior to testing. That is, pressure is maintained at the known pressure for a predetermined length of time. During this time, the temperature and pressure of the fixture, seals, clamps, and part is allowed to reach equilibrium, also known as stabilization. It should be appreciated that the time required for the fixture and related components to reach this equilibrium is directly proportional to the size of the cavity being tested; that is, a larger cavity has a higher heat capacity and, thus, requires longer time to stabilize relative to a smaller cavity.
Once the temperature and pressure of the fixture and related components are stabilized, the part is maintained at the stabilized state and the pressure of the cavity is accurately measured over time. The leak rate out of the pressurized cavity is then calculated by dividing the pressure drop in the cavity (.DELTA.P) by the measured length of time (.DELTA.T). It is assumed that any measured pressure drop in the cavity is attributable to a leak being present in an exposed wall in the part. An exposed wall is defined as a wall that is subjected to a pressure gradient. Finally, the tested cavity is vented to the atmosphere and the test is completed. This testing process may then be repeated for a second part.
For most components produced in large quantities, the pressure decay process requires automated part handling equipment such as transfer lines, robotic manipulation, and/or similar techniques to maintain production levels due to the long test cycle times and single part testing procedures. This automated handling equipment, however, is typically expensive and complex. By way of an example, a typical testing station with a transfer line, sealing rams, and clamping fixtures may cost approximately $200,000. Parts having multiple cavities to be testes would require an additional testing station for each cavity, thereby compounding the cost. Notwithstanding, there is also the additional cost of providing floor space sufficient to accommodate the various testing stations throughout the life of the product.
In an attempt to decrease the cycle time required to perform the testing of a part having multiple cavities, another known pressure decay process employs a single testing station and fixture. If there are no shared walls between the cavities being tested, then the cavities can be tested in parallel without compromise. If there are shared walls, the pressure decay testing process described above is simply repeated in series for each of the multiple cavities. That is, the above described pressure decay process is first completed in its entirety for a first cavity and then completed in its entirety for a second cavity. This insures that any wall shared by adjacent cavities are correctly leak tested because each cavity is tested wholly independent from the other, thus insuring the shared wall is subjected to the correct pressure gradient. It should be appreciated that the cycle time for leak testing multiple cavities reduces the number of parts that can be tested.
Accordingly, there exists a need in the relevant art to provide a method and apparatus for pressure leak testing a part having multiple cavities that overcomes the disadvantages of the prior art. Furthermore, there exists a need in the relevant art to provide a multiple cavity leak test method and apparatus that is capable of minimizing the cycle time associated therewith. Still further, there exists a need in the relevant art to provide a multiple cavity leak test method and apparatus capable of minimizing the cycle time investment and floor space required for testing.